Gas-filled tube



Marsh 29, 1938. D w, BQDLE 2,112,327

GAS -FILLED TUBE Filed March 26, 1955 External Coating 0r Finish 32120]:or O eaqae Glass Envelope INVENTOR fl WBOdfl? ATTORNEY Patented Mar. 29,1938 UNlTED STATES i TENT OFFICE Application March 26, 1935, Serial No.13,172

8 Claims.

This invention relates to gas-filled tubes. More particularly, thisinvention relates to means and methods for reducing and preventinginstability in the properties and operating characteristics ofgas-filled tubes.

Gas-filled tubes generally consist of two or more spaced electrodesenclosed in an envelope, such as glass, filled with a gaseous medium.such as neon, argon, krypton, or helium or a combination of these gases.These electrodes are so spaced within their envelopes that when avoltage exceeding a predetermined value, otherwise known as thebreakdown voltage of the tube, becomes impressed across any two of itselectrodes, a bluish, luminous, gaseous discharge will occur betweenthese electrodes. This luminous discharge will generally continue aslong as a somewhat lower voltage, i. e., the sustaining voltage, remainsimpressed across the aforementioned two electrodes. Immediately upon thedischarge and throughout its duration, the impedance between all of theelectrodes of the tube will be reduced from an almost infinite value toa low and practically negligible value.

It has been discovered that the presence of light and its impressionupon the electrodes contained within the tube materially affects thebreakdown voltage of the tube. It has been further discovered that theeffect of light is generally to reduce the breakdown voltage value. Thechange in the breakdown voltage value has been found to be in difierentand varying degrees which are not readily predeterminable because theyare dependent upon a number of changeable factors which are not easilycontrollable.

In a form of gas-filled tube commercially known as the cold cathodetube, it has been further discovered that the aforementioned reductionin breakdown voltage is most pronounced where such a tube has the upperside of its plate electrode or electrodes coated with an activatingmaterial and the reduction in the breakdown characteristic is especiallymarked in cases where current is passed from the anode of the tube toeither or both of these plate electrodes. It has been determined thatthis activating material reacts to light to a considerable extent andthat the larger the activating surface directly exposed to light, thegreater will be the change in the breakdown voltage of the tube. It hasbeen further determined that the reduction in breakdown voltage is afunction of the intensity of the impressed light as well as of the kindof light, i. e., whether at or near one end of the spectrum or theother, to which the tube may be exposed.

(Cl. ZEN-$57.5)

Ultra-violet rays, for example, have been found to be more effective inreducing the breakdown voltage of the tube than visible rays. Directsunnt will actually reduce the breakdown voltage or a SOO-type of tubeapproximately 25 per cent. 5

Cue of the primary objects of this invention is to reduce or eliminatethe effect of the aforementioned factors upon the breakdown voltage of agas-filled tube.

Another of the objects of this invention is to 10 reduce or eliminatethe undesirable effects of exposure to light upon gas-filled tubes andtheir operating characteristics and properties.

A further object of this invention is to provide means for continuouslymaintaining the break- 15 down voltage of gas-filled tubes highlyconstant.

These and further objects of this invention will be apparent from thedescription hereinafter following when read in connection with theaccompanying drawing in which Figures 1 to 4 20 show four diiierentembodiments of the invention.

Fig. 1 of the drawing shows a gas-filled tube l, the base of which ismounted in a panel 2 of, for example, bakelite, rubber or the like. Thistube is enclosed within a light-proof can 3 which may be of aluminum,tin, copper, or any material which will not transmit light. A metallicor conducting material will be preferred to a non-conducting material,however, for the reason that such a can may be made of a material whichwill electrostatically shield the tube against transient or otherexternal effects. This is important where accuracy and precision in thecontinuous operation of the device are desirable factors.

Fig. 2 shows another embodiment of this invention in which the envelopeof the tube 1 is coated with a light excluding material 5 produced, forexample, by spraying the envelope with bakelite, lacquer or othercompound or paint which is opaque to light, the coating being such thatit will permanently remain affixed to the envelope after it is applied.When so coating the tube envelope, it may be desirable to allow a smallsection 8 thereof, for example, an area V to be uncoated. This uncoatedarea, although not generally necessary, may be desired, however,wherever the elements of the tube or its operation ought to beobservable.

Fig. 3 differs from Fig. 2 in that the envelope of the tube l containingthe gaseous medium is made of a glass or material which excludes lightrays of the visible spectrum as well as all other rays such as those ofthe ultra-violet spectrum. 55

For instance, the envelope may be formed of black glass or any opaquecolored glass.

In Fig. 4 it is proposed to illustrate that the envelope of the tube Imay be made of transparent glass and that either its external surfacedesignated 8 or its internal surface designated 9, or both, may becoated or finished with a light excluding paint or substance such as maybe produced by sand blasting, hydrofluoric acid, or the like.

It will be understood that the metallic can 3 of Fig. 1 may be employedto enclose the tubes of Figs. 2 to 4 for the purpose ofelectrostatically shielding the electrodes of these tubes againstexternal effects.

It is important to note that this invention is primarily concerned witheliminating light from a gas-filled tube so that substantially no lightwhatever external to the tube will reach into the envelope of the tubeand thereby affect its breakdown voltage characteristic by causingionization of the gas therein due to photo-electric effects.

While this invention has been shown and described in certain particulararrangements merely for the purpose of illustration, it will beunderstood that the general principles of this invention may be appliedto other and widely varied organizations without departing from thespirit of the invention and the scope of the appended claims.

What is claimed is:

1. The combination of a gas-filled discharge tube having a plurality ofactivated electrodes which are unheated and means to maintain thebreakdown voltage of the tube nearly constant, said means comprisingmeans to completely exclude light from the interior of said tube.

2. Means for maintaining the breakdown voltage of a gas-filled tubenearly constant and unaffected by external rays of light comprising acoating applied to the envelope of the tube to render the envelopeopaque to light.

3. A gas-filled discharge tube having a glass envelope enclosing onlynormally cold electrodes,

said envelope being externally coated by a substance which is opaque tolight so as to maintain the breakdown voltage of the tube substantiallyconstant.

4. In a gas-filled tube, means for maintaining the operatingcharacteristics of said gas-filled tube nearly constant and independentof external conditions comprising a coating applied to one of the sidesof the envelope of said tube, said coating being impervious to light,

5. The combination of a gas discharge tube within the envelope of whichare at least two activated electrodes between which a predeterminedpotential must be impressed before gaseous ionization takes placetherebetween, and means for maintaining the breakdown voltage betweensaid two electrodes constant during varying external light conditions,said means comprising a light opaque coating about the envelope of saidtube.

6. The combination of a gas-filled tube having activated electrodes andmeans comprising a metallic shield enclosing the tube to shield saidelectrodes from external capacity effects and to maintain a dark spaceabout said tube so that the breakdown voltage between the electrodes ofthe tube will be highly constant.

*7. Means to eliminate external capacity variations from a gas-filledtube and to maintain a substantially constant breakdown voltage betweenthe electrodes of the tube comprising a metallic shield enclosing thetube to prevent light external of the tube from reaching the electrodesof the tube and from affecting the breakdown voltage between saidelectrodes.

8. The combination of two spaced electrodes enclosed within an envelopefilled with gas, the breakdown voltage between said electrodes beingvariable according to different light conditions and being influenced byexternal capacity effects, and a metallic enclosure for said envelope toeliminate from the electrodes within said envelope all external lightand to shield said electrodes from external electrostatic fields.

DAVID W. BODLE.

